1. Field of the Invention
The present invention relates to materials on which images such as letters and figures are to be written or printed with a recording liquid. Hereinafter, the materials are simply referred to as recording materials.
2. Description of the Prior Art
Recording with a recording liquid or ink has long been made by means of writing tools such as pens, fountain pens, felt pens, etc. Recently, so-called ink-jet recording systems have been developed, where ink is also utilized.
The ink-jet recording system makes a record by forming ink droplets by any of a variety of ink-jetting processes (e.g. electrostatic attractive process, mechanical vibration or displacement process by use of piezoelements, bubbling process where bubbles are generated by impulsive heating, etc.), and leading parts or all of the droplets to adhere onto recording materials such as paper.
For such recording processes using liquid ink, ink is generally required not to blot on recording paper so that the printed letters or figures may not become obscure. The ink is also desired to dry so quickly as to prevent the recording paper from incidental staining with undried ink, and the coloring matter of ink fixed on the paper is desired not to fade out as long as possible.
In particular, the ink-jet recording system should satisfy the following requirements:
(1) Ink is quickly absorbed into recording paper. PA1 (2) An ink dot, when overlapping a previously applied ink dot, does not destroy or diffuse the previous ink dot, even in multicolor or full-color recording. PA1 (3) Ink dots do not diffuse on recording paper and therefore are not enlarged more than needed. PA1 (4) The shapes of ink dots are close to a perfect circle and the perimeters of ink dots have smooth lines. PA1 (5) Ink dots have high optical density and distinct perimeter lines. PA1 (6) Recording paper has a high whiteness and a good contrast of ink dots. PA1 (7) The color of ink does not vary depending upon the recording paper used. PA1 (8) Ink droplets scarcely scatter around the dots they form. PA1 (9) Recording paper exhibits a high dimensional stability without being elongated or wrinkled after recording.
While it has been understood that the satisfying these requirements is also due to characteristics of the recording paper, in practice there has hitherto not been plain paper or specially finished paper that meets the above requirements. For example, the specially finished paper for ink-jet recording disclosed in Japanese Patent Kokai No. 74340/1977, though exhibiting a rapid absorption of ink, is liable to enlarge the diameters of ink dots and to make dim the perimeters of ink dots, and it exhibits a significant change in dimensions after recording.